Monte Carlo simulations and analytical approximations for a primitive model of the metal/solid electrolyte interface are presented. The mobile positive and negative point charges in the solid electrolyte are restricted to the corresponding sites of a NaCl lattice (Schottky defects). Single imaging of the mobile charges in the metal was considered. This model of the metal/solid electrolyte interface differs substantially from the primitive model metal/liquid electrolyte interface as a direct result of the discrete spatial locations available to the charges. When the temperature or the dielectric constant of the electrolyte is high, the potential and charge decay monotonically with distance from the interface. The diffuse layer is however less evident than in an analogous primitive model of the metal/liquid electrolyte interface. At high values of the ratio (qe)(2)/T epsilon, an oscillation in the charge density profile is observed as in primitive model simulations of liquid electrolytes, This phenomenon is however more marked for solid electrolytes, which can be rationalized in terms of the discrete spatial locations occupied by the charges in the electrolyte, As a direct consequence of the charge oscillation, the interfacial capacitance may exceed the Helmholtz capacitance calculated using the lattice parameters of the solid electrolyte, a phenomenon which has been observed experimentally.(16-18) The Monte Carlo data can be fitted approximately by a simple modification of the Poisson-Boltzmann equation in which an exponentially decaying function of distance proportional to the total interfacial potential drop is added to the potential in the Boltzmann factor.